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Chapter 4 Section 2 Notes - Overview of Photosynthesis Plants are producers – they produce their own source of energy. Photosynthesis – the process by which light energy is converted to chemical energy; produces sugar and oxygen from carbon dioxide and water – takes place in chloroplasts Chlorophyll – molecule in chloroplasts that absorbs some of the energy in visible light (made of different wavelengths or colors of light) Plants use energy in visible light for photosynthesis * 2 Main parts of chloroplasts are needed for photosynthesis: 1. grana (granum, singular) – stacks of compartments called thylakoids – shaped like coins, flat and circular and they are enclosed by membranes that contain chlorophyll 2. stroma – fluid that is all around the grana inside the chloroplast 2 stages of photosynthesis: 1. Light-dependent reactions – capture energy from sunlight takes place in the thylakoids and their membranes - chlorophyll absorbs energy from sunlight, energy moves along the thylakoid membrane and is transferred to molecules that carry energy, such as ATP - during this process H2O molecules are broken down and O2 molecules are released 2. Light-independent reactions – use the energy from the lightdependent reactions to make sugars (Calvin Cycle) takes place in the stroma - CO2 and energy from the light-dependent reactions are used to build sugars, usually glucose (C6H12O6) 6CO2 + 6H2O + light energy ----- C6H12O6 + 6O2 Carbon + water + light energy ------ a sugar + oxygen Dioxide * Plants often use the simple sugars produced by photosynthesis to build starch and cellulose molecules.